Interpretive Summary: The benefits of applying livestock manure to crops have been recognized for centuries. However, nutrient composition of manure varies with a number of factors, including animal type, bedding, feed ration, storage/handling, environmental conditions, field application method, and age of manure, so that quantifying the nutrient value of applied manure remains a complex challenge. In response, a multi-regional soil testing workgroup has developed a manure testing manual. Work on the manual focused on four main areas: sampling, analytical procedures, quality control in the laboratory, and reporting. The analytical section includes suggested methods for determining elemental concentrations in extracts and digests of manures. This information is a valuable resource for any laboratory that analyzes manures for nutrient content.

Technical Abstract:
Spectrochemical methods have been used for many years to determine elemental concentrations in extracts and digests of soils, plant tissue, manures, composts, and other materials. In this chapter, three such methods for the determination of elemental concentrations in manure digests are discussed. Although a number of other techniques are available, atomic absorption spectroscopy, inductively coupled plasma-atomic emission spectroscopy, and colorimetry are the methods most commonly used by public and private laboratories. Atomic absorption spectroscopy can be used to determine the concentration of most elements of interest, with phosphorus being the exception. Inductively coupled plasma-atomic emission spectroscopy is the method of choice for the analysis of manure digests. The technique has excellent sensitivity coupled with a usable linear concentration range of four to five orders of magnitude for most elements of interest. The classical colorimetric procedure for the determination of phosphorus is still used, although many laboratories have automated the procedure with either an AutoAnalyzer or flow injection system. This information is a valuable resource for any laboratory that analyzes manures for nutrient content.